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武藤 巧*; 丸山 敏毅; 巽 敏隆*
Symmetry (Internet), 17(2), p.270_1 - 270_24, 2025/02
被引用回数：1 パーセンタイル：26.70(Multidisciplinary Sciences)Kaon condensation in hyperon-mixed matter, [(
) phase] which may be realized in neutron stars, is discussed on the basis of chiral symmetry. With the use of the effective chiral Lagrangian for kaon-baryon and kaon-kaon interactions; coupled with the relativistic mean field theory and universal three-baryon repulsive interaction, we clarify the effects of the 
-wave kaon-baryon scalar interaction simulated by the kaon-baryon sigma terms and vector interaction (Tomozawa-Weinberg term) on kaon properties in hyperon-mixed matter, the onset density of kaon condensation, and the equation of state with the () phase. In particular, the quark condensates in the () phase are obtained, and their relevance to chiral symmetry restoration is discussed.
Xia, C.-J.*; 丸山 敏毅; 安武 伸俊*; 巽 敏隆*
Physical Review D, 110(11), p.114024_1 - 114024_14, 2024/12
被引用回数：3 パーセンタイル：37.77(Astronomy & Astrophysics)Based on an extended Nambu-Jona-Lasinio model that treats baryons as clusters of quarks, we investigate the properties and microscopic structures of mixed phases for various types of first-order phase transitions in a unified manner, where the model parameters are fixed by reproducing nuclear matter properties and the binding energies of finite nuclei. In particular, based on the Thomas-Fermi approximation, we investigate the mixed phases that arise from the liquid-gas phase transition of nuclear matter, chiral phase transition, and deconfinement phase transition in dense stellar matter adopting spherical and cylindrical approximations for the Wigner-Seitz cells. It is found that the geometrical structures do not emerge for the chiral phase transition, while the droplet, rod, slab, tube, and bubble phases emerge sequentially as density increases for the liquid-gas and deconfinement phase transitions. Additional attractive interactions between strange quark matter and hyperons are observed as the deconfinement phase transition is entangled with the chiral phase transition of quarks. The results obtained here should be useful to understand the properties and structures of dense stellar matter throughout compact stars and, in particular, the matter state in the core regions. Meanwhile, more extensive investigations in a three-dimensional geometry with large box sizes are necessary for our future study.
Xia, C.-J.*; 丸山 敏毅; 安武 伸俊*; 巽 敏隆*; Zhang, Y.-X.*
Nuclear Physics Review, 41(3), p.818 - 827, 2024/09
Based on the relativistic mean field (RMF) model with Thomas-Fermi approximation, we investigate the elastic properties of neutron star matter. The elastic constants are estimated by introducing deformations on the nuclear pasta structures in 
-equilibrium, where various crystalline configurations are considered in a fully three-dimensional geometry without the Wigner-Seitz approximation. Two scenarios with different symmetry energy slope (
=41.34 and 89.39 MeV) are examined, where the elastic constants can vary by ten times. By fitting to the numerical results, we improve the analytic formulae for the elastic properties of nuclear pasta by introducing damping factors.
丸山 敏毅; 安武 伸俊*
Nuclear Physics Review, 41(3), p.806 - 810, 2024/09
We present a microscopic simulation of particles with time-dependent spins, where different interaction and density are considered. Ferromagnetism has been observed for the attractive spin-spin interaction, while antiferromagnetism and paramagnetism have been observed in different density region for the repulsive spin-spin interaction. The method developed here should be extended to include spin-color interaction into "color molecular dynamics".
安武 伸俊*; 丸山 敏毅
Nuclear Physics Review, 41(3), p.801 - 805, 2024/09
We present the current status of molecular dynamics, in which hadron and quark matter are described only within quark models. In our previous calculations, we solved the time evolution of internal degrees of freedom for color. In this article, we show the results simultaneously solved the internal degrees of freedom for spin as well. Unlike conventional methods, our approach also considers the flavor conversion between quarks and electrons during the calculations, which naturally achieves the beta equilibrium under the charge neutrality condition. Based on this latest formulation, the equation of state for dense matter is studied, replicating the saturation properties: symmetric energy, -parameter, incompressibility around nuclear density. The resultant mass-radius relations are also consistent with the observations such as the gravitational wave observations, and NICER. Our numerical results suggest that deconfined quark matter appears in the core of neutron stars via crossover. The key difference from previous molecular dynamics simulations is the spontaneous emergence of clustering of quarks or baryons on a local scale. These properties would never be observed in equations of state based on the other approaches. While our formulation does not yet fully include strangeness, we expect that our method has a possibility to show the direct evidence of the quark clustering models such as "the strangeon model" or "the sexaquark model".
安武 伸俊*; 丸山 敏毅
Physical Review D, 109(4), p.043056_1 - 043056_11, 2024/02
被引用回数：2 パーセンタイル：26.79(Astronomy & Astrophysics)The equation of state for dense matter is studied with colour molecular dynamics, in which hadron matter and quark matter are automatically distinguished only from quark colour state. The quark-quark interactions are optimized to be consistent with saturation properties: symmetric energy, -parameter, and incompressibility around nuclear density. In the calculations, the degrees of freedom of colours are solved at each numerical step, although the flavours are fixed as up or down quarks. The resultant mass-radius relations of neutron stars also satisfy the observational constraints. In this model deconfined quark matter appears in the core of neutron stars via crossover. Although the current constraints from the observations are not enough to conclude whether quark matter appears at high-density region, our method would help to understand high-density material properties inside neutron stars.
Xia, C.-J.*; 丸山 敏毅; 安武 伸俊*; 巽 敏隆*; Zhang, Y.-X.*
Physics Letters B, 839, p.137769_1 - 137769_5, 2023/04
被引用回数：5 パーセンタイル：58.11(Astronomy & Astrophysics)Realistic estimations on the elastic properties of neutron star matter are carried out with a large strain (
0.5) in the framework of relativistic-mean-field model with Thomas-Fermi approximation, where various crystalline configurations are considered in a fully three-dimensional geometry with reflection symmetry. Our calculation confirms the validity of assuming Coulomb crystals for the droplet phase above neutron drip density, which nonetheless does not work at large densities since the elastic constants are found to be decreasing after reaching their peaks. Similarly, the analytic formulae derived in the incompressible liquid-drop model give excellent description for the rod phase at small densities, which overestimates the elastic constants at larger densities. For slabs, due to the negligence on the variations of their thicknesses, the analytic formulae from liquid-drop model agree qualitatively but not quantitatively with our numerical estimations. By fitting to the numerical results, these analytic formulae are improved by introducing dampening factors. The impacts of nuclear symmetry energy are examined adopting two parameter sets, corresponding to the slope of symmetry energy L = 41.34 and 89.39 MeV. Even with the uncertainties caused by the anisotropy in polycrystallines, the elastic properties of neutron star matter obtained with L = 41.34 and 89.39 MeV are distinctively different, results in detectable differences in various neutron star activities.
Xia, C.-J.*; 丸山 敏毅; 安武 伸俊*; 巽 敏隆*
Physical Review D, 106(6), p.063020_1 - 063020_14, 2022/09
被引用回数：10 パーセンタイル：55.35(Astronomy & Astrophysics)We study nuclear pasta structures at high temperatures within a relativistic mean field model and Thomas-Fermi approximation. Typical structures (droplet, rod, slab, tube, and bubble) are obtained, which form various crystalline configurations. The properties of those nuclear pastas are examined in a three-dimensional geometry with reflection symmetry, where the optimum lattice constants are fixed minimizing the free energy under spherical or cylindrical approximations for Wigner-Seitz cells. For fixed densities and temperatures, the differences of the free energies per baryon for various shapes and lattice structures are typically on the order of tens of keV, suggesting the coexistence of those structures. If we further increase temperature, eventually the non-uniform structures of nuclear pasta become unstable and are converted into uniform nuclear matter. The phase diagrams of nuclear matter are estimated, which is useful for understanding the various phenomena in neutron stars.
武藤 巧*; 丸山 敏毅; 巽 敏隆*
Progress of Theoretical and Experimental Physics (Internet), 2022(9), p.093D03_1 - 093D03_37, 2022/09
被引用回数：3 パーセンタイル：30.27(Physics, Multidisciplinary)The possible coexistence of kaon condensation and hyperons in highly dense matter is investigated. Two coupling schemes for the s-wave kaon-baryon interaction are compared regarding the onset density of kaon condensation in hyperon-mixed matter and the equation of state for the developed () phase. One is the contact interaction scheme related to the non-linear effective chiral Lagrangian. The other is the meson exchange scheme. It is shown that in the meson exchange scheme, the contribution from the non-linear scalar self-interaction gives rise to a repulsive effect for the kaon effective energy, pushing up the onset density of kaon condensation. The non-linear self-interacting term is not relevant to repulsive energy leading to stiffening of the EOS at high densities, and it cannot be compensated with a large attractive energy due to the appearance of the () phase in the case of the contact interaction scheme.
Xia, C.-J.*; 丸山 敏毅; Li, A.*; Sun, B. Y.*; Long, W.-H.*; Zhang, Y.-X.*
Communications in Theoretical Physics, 74(9), p.095303_1 - 095303_15, 2022/08
被引用回数：39 パーセンタイル：92.33(Physics, Multidisciplinary)In the framework of the Thomas-Fermi approximation, we study the EOSs and microscopic structures of neutron star matter in a vast density range with 
-
, where various covarriant density functionals are adopted, i.e., those with nonlinear self couplings (NL3, PK1, TM1, GM1,MTVTC) and density-dependent couprings (DD-LZ1, DDME-X, PKDD, DD-ME2, DD2, TW99)It is found that the EOSs generally coincide with each other at 
fm
and 
fm
fm, while in other density regions they are sensitive to the effective interactions between nucleons. By adopting functionals with a larger slope of symmetry energy the curvature parameter 
and neutron drip density generally increases, while the droplet size, proton number of nucleus, core-crust transition density and onset density of non-spherical nuclei, decrease. All functionals predict neutron stars, with maximum masses exceeding the two-solar-mass limit, while those of DD2, DD-LZ2, DD-ME2, and DDME-X predict optimum neutron star radii according to the observational constraints. Nevertheless, the corresponding skewness coefficients 
are much larger than expected, while only the functionals MTVTC and TW99 meet the start-of-art constraints on . More accurate measurements on the radius of PSR J0740+6620 and the maximum mass of neutron stars are thus essential to identify the functional that satisfies all constraints from nuclear physics and astrophysical observations. Approximate linear correlations between neutron stars' radii at 
and 
, the slope and curvature parameter of symmetry energy are adopted here. The results presented here are applicable for investigations of the structures and evolutions of compact stars in a unified manner.
大島 宏之; 森下 正樹*; 相澤 康介; 安藤 勝訓; 芦田 貴志; 近澤 佳隆; 堂田 哲広; 江沼 康弘; 江連 俊樹; 深野 義隆; et al.
Sodium-cooled Fast Reactors; JSME Series in Thermal and Nuclear Power Generation, Vol.3, 631 Pages, 2022/07
ナトリウム冷却高速炉(SFR: Sodium-cooled Fast Reactor)の歴史や、利点、課題を踏まえた安全性、設計、運用、メンテナンスなどについて解説する。AIを利用した設計手法など、SFRの実用化に向けた設計や研究開発についても述べる。
Miao, Z.-Q.*; Xia, C.-J.*; Lai, X.-Y.*; 丸山 敏毅; Xu, R.-X.*; Zhou, E.-P.*
International Journal of Modern Physics E, 31(4), p.2250037_1 - 2250037_20, 2022/04
被引用回数：18 パーセンタイル：86.66(Physics, Nuclear)It is suggested that pulsar-like compact stars are comprised entirely of strangeons (quark-clusters with three-light-flavor symmetry) and a small amount of electrons. To constrain the properties of strangeon stars, we propose a linked bag model to describe matter with the strong interaction in both 2-flavored (nucleons) and 3-flavored (hyperons, strangeons, etc.) scenarios. The parameters are calibrated to reproduce the saturation properties of nuclear matter. The energy per baryon of strangeon matter is smaller than that of baryon matter if the strangeon carries a large number of valence quarks, which stiffens the equation of state and consequently increases the maximum mass of strangeon stars. The maximum mass and tidal deformability of strangeon stars within the present model are consistent with the observation, i.e. the maximum mass of strangeon stars can be 
2.5 solar mass, and the tidal deformability of a 1.4 solar mass star can be 
.
Xia, C.-J.*; Sun, B. Y.*; 丸山 敏毅; Long, W.-H.*; Li, A.*
Physical Review C, 105(4), p.045803_1 - 045803_14, 2022/04
被引用回数：24 パーセンタイル：92.65(Physics, Nuclear)Assuming spherical and cylindrical approximations for the Wigner-Seitz cell, typical nuclear matter structures (droplet, rod, slab, tube, bubble, and uniform) are observed. We then investigate the equations of state and microscopic structures of nuclear matter with both fixed proton fractions and beta equilibration, where two covariant density functionals, DD-LZ1 and DD-ME2, are adopted. Despite the smaller slope of symmetry energy obtained with the functional DD-LZ1, the curvature parameter is much larger than that of DD-ME2. Consequently, different mass-radius relations of neutron stars are predicted by the two functionals. Different microscopic structures of non-uniform nuclear matter are obtained as well, which are expected to affect various physical processes in neutron star properties and evolutions.
武藤 巧*; 丸山 敏毅; 巽 敏隆*
Physics Letters B, 820, p.136587_1 - 136587_6, 2021/09
被引用回数：16 パーセンタイル：78.89(Astronomy & Astrophysics)相対論的平均場理論(RMF)の枠組みで
中間子場の非線形ポテンシャルを用いずに、バリオン間普遍3体斥力(UTBF、核子系ではTNRと略記)、及び核物質の飽和密度
近傍で引力的に作用する核子3体力(TNA)を現象論的に導入し、対称核物質の飽和性とでの非圧縮率、対称エネルギーの実験値を再現するように定めた。このような条件のもとでは、中性子物質のslope parameter が高密度での状態方程式と強く関連していることが分かった。これを用いて(hyperon+
)相の状態方程式を求め、重い中性子星質量の観測と矛盾せずに、高密度星の内部構造を(hyperon+)相を含むハドロン物質描像で説明できることを示した。
Xia, C.-J.*; 丸山 敏毅; 安武 伸俊*; 巽 敏隆*; Zhang, Y.-X.*
Physical Review C, 103(5), p.055812_1 - 055812_13, 2021/05
被引用回数：21 パーセンタイル：86.64(Physics, Nuclear)In the framework of the relativistic mean field model with Thomas-Fermi approximation, we study the structures of low density nuclear matter in a three-dimensional geometry with reflection symmetry. The effect of finite cell size is treated carefully by searching for the optimum cell size. Typical pasta structures (droplet, rod, slab, tube, and bubble) arranged in various crystalline configurations are obtained for both fixed proton fractions and -equilibration. It is found that the properties of droplets/bubbles are similar in body-centered cubic (BCC) and face-centered cubic (FCC) lattices, where the FCC lattice generally becomes more stable than BCC lattice as density increases. For the rod/tube phases, the honeycomb lattice is always more stable than the simple one. By introducing an 
-
cross coupling term, we further examine the pasta structures with a smaller slope of symmetry energy 
MeV, which predicts larger onset densities for core-crust transition and non spherical nuclei. Such a variation due to the reduction of is expected to have impacts on various properties in neutron stars, supernova dynamics, and binary neutron star mergers.
Xia, C.-J.*; 丸山 敏毅; 安武 伸俊*; 巽 敏隆*; Shen, H.*; 富樫 甫*
Physical Review D, 102(2), p.023031_1 - 023031_18, 2020/07
被引用回数：34 パーセンタイル：80.64(Astronomy & Astrophysics)高密度星を構成する物質のクォーク-ハドロン混合相について調べる。クォーク相とハドロン相はそれぞれいくつかのモデルにより計算し、混合相の形状と状態方程式については、Ravenhallらによる連続的な幾何学的次元による計算法を踏襲する。その際表面張力は固定した値のものの他、多重反射展開法によるものと、equivparticle法によるものとを使う。これによって天体の全体的構造や質量,半径などが得られる。天体の半径と潮汐変形性の相関はハイブリッド星でも中性子星のときと同様であった。重い天体になると中心付近にクォーク物質が現れ、クォーク-ハドロンの境界の表面張力が全体の構造に対して重要になる。0.8fm以下の密度では観測量により状態方程式に対する制限が良く得られるが、高密度では不定性が大きかった。
武藤 巧*; 丸山 敏毅; 巽 敏隆*; 高塚 龍之*
JPS Conference Proceedings (Internet), 26, p.024019_1 - 024019_4, 2019/11
The equation of state with coexistent phase of kaon condensation and hyperons [the (
) phase] in highly dense matter is constructed so as to be consistent with the recent observations of massive neutron stars. The nonlinear effective chiral Lagrangian is combined with the relativistic mean-field theory. The universal three-body repulsive force is further introduced based on the string-junction model. It is shown that the stiff equation of state with the () phase, leading to the maximum mass of neutron stars as large as two solar mass, can be obtained for the larger value of the range parameter of the repulsive core included in the string-junction model. Some problems to be resolved such as causality are mentioned.
Maslov, K.*; 安武 伸俊*; Blaschke, D.*; Ayriyan, A.*; Grigorian, H.*; 丸山 敏毅; 巽 敏隆*; Voskresensky, D. N.*
Physical Review C, 100(2), p.025802_1 - 025802_11, 2019/08
被引用回数：64 パーセンタイル：97.12(Physics, Nuclear)ハドロン-クォーク相転移に対するパスタ相の及ぼす影響を、相対論的平均場による状態方程式に関してしらべた。パスタ相の存在をフルに考慮した数値計算による状態方程式と従来の2相の内挿による混合相の状態方程式を比較した。ハドロン相・クォーク相双方に対して混合相の状態方程式がMaxwell構成法とほぼ一致する表面張力の限界値が得られた。そしてその値は理論による推定値とよく一致した。また、ベータ平衡な中性子星物質まで理論を拡張することで、ハイブリッド高密度星の構造と第3系列のロバストネスに対するパスタ相の影響を議論した。
Xia, C.-J.*; 丸山 敏毅; 安武 伸俊*; 巽 敏隆*
Physical Review D, 99(10), p.103017_1 - 103017_14, 2019/05
被引用回数：36 パーセンタイル：78.76(Astronomy & Astrophysics)We study the interface effects of a quark-hadron mixed phase in compact stars. The properties of nuclear matter are obtained based on the relativistic-mean-field model. For the quark phase, we adopt a perturbation model with running quark masses and coupling constant. At certain choices of parameter sets, it is found that varying the quark-hadron interface tension will have sizable effects on the radii (
m) and tidal deformabilities (
%) of 1.36 solar mass hybrid stars. These provide possibilities for us to constrain the quark-hadron interface tension with future gravitational wave observations as well as the ongoing NICER mission.
丸山 敏毅; 武藤 巧*; 巽 敏隆*
JPS Conference Proceedings (Internet), 20, p.011043_1 - 044043_3, 2018/01
It is well-known that mixture of hyperons and kaons in nuclear matter cause softening of matter due to a strong attraction or increased number of degree of freedom. This softening is one of the most serious problems in nuclear physics since one has to sustain an observed heavy neutron star with twice the solar mass. On the other hand, we have investigated the competition of kaon and hyperon mixture in nuclei. Then we found that all the kaons put in nuclei are absorbed in nucleons and converted into hyperons. In the case of nuclear matter in the core of neutron stars, where baryon chemical potential gets high due to the compression of matter, different aspects are observed: hyperons (mainly 
) are mixed to reduce baryon chemical potential. With the appearance of kaons, however, repulsion between kaons and hyperons makes the hyperon fraction to decrease. If we take account of inhomogeneous matter, we found that kaons and hyperons distribute separately.
